In part from a thing I wrote on usin PS IR and edited for this discussion ...
To use the 2 images that you have ... in a folder ... (the 2 images must be together in their own folder) ...
"Open Image Ready. Click on File > Import > Folder as Frames. Navigate to this folder and click ok .Now one of the images that is in this folder will appear at the top of the work area, and both of the images will appear in the animation palette at the bottom left of the work area.
The image on the left (#1) should be highlighted. If its not go ahead and highlight it. Whichever image in the animation palette is highlighted that is the one that will appear at the top of your work area.
With that image highlighted there is a tiny arrow (>) towards the top right hand side of the animation palette just beneath the x. Click on that tiny arrow and a menu will pop up. Scroll up the menu and choose Tween. Choose Tween With “Next Frame” from the drop down box. Choose 3 as the “Frames to Add”. Click ok.
Next highlight the last frame (#5) and click on that arrow again. Scroll up the menu and select Tween again. Choose Tween with "First Frame". Select Frames to add “3”,again. Click ok.
Now click on the “play” button to view the animation. You can click on each frame where it says “0 sec.” To change the time that each frame is displayed during the animation. Have fun.
If you want to use this on the web you may want to save this to a gif image. Click on File > Saved Optimized As. Choose a name and Images only *.gif. Click on Save.